As many as 20 officers at the federal prison in Manhattan where Jeffrey Epstein killed himself have been subpoenaed.

Federal investigators sought the grand jury subpoenas as they try to piece together the events leading up to Epstein’s suicide at the Metropolitan Correctional Center earlier this month, according to CNN.

Two guardsmen who were tasked with watching Epstein are of particular interest to investigators. The pair, who have been placed on leave, are suspected to have fallen asleep on the job when Epstein died.

Attorney General William Barr ordered the FBI and the Justice Department’s inspector general to investigate both Epstein’s Aug. 10 suicide, as well as his previous attempt on July 23, when he was found nearly unconscious on his cell floor with marks on his neck.

The 66-year-old millionaire, a convicted sex offender who was awaiting trial for child sex trafficking and conspiracy charges, was found unresponsive in his cell in the special housing unit after being taken off suicide watch. The New York City medical examiner’s office officially ruled Epstein’s death a suicide on Friday following an autopsy. He appeared to have tied a bedsheet to the top of a bunk bed and then moved toward the floor with enough force to break a bone in his neck.

Barr said he was “appalled” to learn of Epstein’s death and expressed deep concern about “serious irregularities” at the Metropolitan Correctional Center in New York.

Numerous reports have emerged about guards not being properly trained, doing overtime shifts multiple days in a row, falling asleep on the job, and potentially falsifying records about how often Epstein was being checked.

Lamine N’Diaye, who was the warden of the Metropolitan Correctional Center at the time of Epstein’s death, was temporarily reassigned by Barr and has been replaced by Kathleen Hawk Sawyer, who previously served as director.

Barr told reporters in Dallas on Wednesday that his investigation is moving “expeditiously” and expects to report his findings soon to both Congress and the public.